Several Brassica species are recognized as an increasingly important oilseed crop and a source of high quality protein meal in many parts of the world. The oil extracted from the seeds commonly contains a lesser concentration of endogenously formed saturated fatty acids than other vegetable oils and is well suited for use in the production of salad oil or other food products or in cooking or frying applications. The oil also finds utility in industrial applications. Additionally, the meal component of the seeds can be used as a nutritious protein concentrate for livestock.
The three primary Brassica species currently utilized for Brassica production and development are Brassica napus, Brassica rapa and Brassica juncea, each of which belong to the family Brassicaceae. Brassica juncea is currently grown as an oilseed in India and China. As Brassica juncea tolerates heat and drought conditions to a greater extent than Brassica napus and Brassica rapa, there is potential for Brassica juncea production in certain areas of the United States, Canada and Australia. Table 1 contains a comparative description of the general characteristics of Brassica napus, Brassica rapa and Brassica juncea compiling information from the Canola Council of Canada worldwide web site and the USDA circular number C857 by Albina Musil USDA1950C857 (1951).
Brassica juncea is commonly grown as a condiment mustard species in several countries including Canada, Hungary, Poland, Ukraine, China, Nepal and India. Mustard quality Brassica juncea is typically high in glucosinolate and high in erucic acid content, but is relatively low in oil content. Mustard seed can be used in whole seed or crushed form. Seed may be milled into flour or the oil may be extracted for use in cooking. High glucosinolate and high erucic acid types are quality variants within the same species, differing only in quality parameters. As a result, cross breeding between low and high glucosinolate or erucic acid genotypes are easily made.
Certain genotypes of Brassica juncea generally possess relatively low erucic acid levels in the oil and low glucosinolate levels in the meal. Therefore, certain commercial varieties of Brassica juncea may be developed that can be termed “CANOLA®” in accordance with the trademark of the Canola Council of Canada, which refers to forms of oilseed Brassica with erucic acid of <2% in the oil and total glucosinolates of <30 micromoles/gram of defatted meal.
TABLE 1Key morphological differences separating Brassica napus, Brassicajuncea and Brassica rapa oilseeds and mustardsTrait/SpeciesBrassica napusBrassica junceaBrassica rapaGrowth habitSpring and WinterSpringSpring and WinterCotyledonSmooth on undersideSmall - 5/16 to 9/16 inch acrossSpiny and wrinkled onmorphologyLarge - ⅝ to ⅞ inches acrossLess lobed than napus - lighterundersideHeart-shaped cotyledon andgreen colorSmall - 5/16 to 9/16 inchdark green in coloracrossLess lobed than napus -lighter green colorFirst leafOblong or shield shaped,Oblong, bright green and hairyOblong, bright green to lightmorphologythin, bluish-green in color,bluish-green, sparingly hairysmooth with a few hairs nearthe marginFlowersBuds borne above open flowersOpen flowers borne above budsCompact bud clusters, budsheld below uppermost openflowersPollinationPrincipally self-pollinatingPrincipally self-pollinating andPrincipally cross-pollinatedand mostly self-compatiblemostly self-compatibleand self-incompatible(although there is one self-pollinating, self-compatiblevariety known as Yellowsarson)Leaf morphologyLeaf blade only partiallySmall petiole attaches leaf to stemLeaf blade clasps stemclasps stemMargins with irregular shallowcompletelyLyrate in formindentationsRoughly oblong withcoarsely toothed marginsSeed colorBlackBrown and/or yellowBrown and/or yellowPloidyAmphidiploid (AACC)Amphidiploid (AABB)Diploid (AA)2 copies of rapa genome2 copies of rapa genome (AA)2 copies of rapa genome (AA)(AA)2 copies of nigra genome (BB)2 copies of oleraceae genome(CC)The genomic composition of canola species are as follows (FIG. 1). Brassica rapa, a diploid species, contains only the A (rapa) genome and has a genomic constitution of AA. Brassica napus is an amphidiploid with the rapa (A) and oleraceae (C) genomes and is listed as AACC. Brassica juncea is also an amphidiploid with the rapa (A) genome and the nigra (B) genome. Genetically, Brassica juncea is listed as AABB.
During pollen and ovule formation, the chromosomes within each genome will pair with their homologues (i.e., ‘A’ chromosomes will pair with ‘A’, ‘B’ will pair with ‘B’), and it is extremely rare to have pairing of A and B or A and C. This pairing may be forced by repeated crossing and careful selection of plant phenotype during breeding, although there is no expectation that a trait from one genome may be combined with a trait from the other genome.
Brassica sp. cultivars are developed through breeding programs that utilize techniques such as mass and recurrent selection, backcrossing, pedigree breeding and haploidy. Recurrent selection is used to improve populations of either self or cross-pollinating Brassica. Through recurrent selection, a genetically variable population of heterozygous individuals is created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes.
Breeding programs use backcross breeding to transfer genes for a simply inherited, highly heritable trait into another line that serves as the recurrent parent. The source of the trait to be transferred is called the donor parent. After the initial cross, individual plants possessing the desired trait of the donor parent are selected and are crossed (backcrossed) to the recurrent parent for several generations. The resulting plant is expected to have the attributes of the recurrent parent and the desirable trait transferred from the donor parent. This approach has been used for breeding disease resistant phenotypes of many plant species. However, certain traits are difficult to transfer by backcross breeding because other attributes of the recurrent parent are linked to the desirable trait, and therefore it is difficult to develop a resulting plant with all of the attributes of the recurrent parent and the desirable trait transferred from the donor parent. Backcrossing has been used to transfer low erucic acid and low glucosinolate content into lines and breeding populations of Brassica. 
Pedigree breeding and recurrent selection breeding methods are used to develop lines from breeding populations. Pedigree breeding starts with the crossing of two genotypes, each of which may have one or more desirable characteristics that is lacking in the other or which complements the other. If the two original parents do not provide all of the desired characteristics, other sources can be included in the breeding population. In the pedigree method, superior plants are selfed and selected in successive generations. In the succeeding generations the heterozygous condition gives way to homogeneous lines as a result of self-pollination and selection. Typically in the pedigree method of breeding five or more generations of selfing and selection is practiced: F1 to F2; F2 to F3; F3 to F4; F4 to F5, etc. For example, two parents that are believed to possess favorable complementary traits are crossed to produce an F1. An F2 population is produced by selfing one or several F1's or by intercrossing two F1's (i.e., sib mating). Selection of the best individuals may begin in the F2 population, and beginning in the F3 the best individuals in the best families are selected. Replicated testing of families can begin in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7), the best lines or mixtures of phenotypically similar lines commonly are tested for potential release as new cultivars. Backcrossing may be used in conjunction with pedigree breeding; for example, a combination of backcrossing and pedigree breeding with recurrent selection has been used to incorporate blackleg resistance into certain cultivars of Brassica napus. 
Plants that have been self-pollinated and selected for type for many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny. If desired, the haploidy method can also be used to extract homogeneous lines. A cross between two different homozygous lines produces a uniform population of hybrid plants that may be heterozygous for many gene loci. A cross of two plants each heterozygous at a number of gene loci will produce a population of hybrid plants that differ genetically and will not be uniform.
The choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F1 hybrid cultivar, pureline cultivar, etc.).